This invention relates to an electric motor protector sensor, and more particularly, an electric motor protector sensor positioned in the motor windings of a sealed compressor motor.
It is known in the art to use a motor protector sensor using a thermistor disposed in an opening in a thin inner layer of insulating material to expose portions of the thermistor on opposite sides of the insulating layer, outer thin layers of similar insulating material are provided with copper foils which are deposited thereon. These outer insulating layers are arranged to sandwich the inner insulating layers, the deposited copper foils carried by the outer insulating layers typically are soldered to respective exposed portions of the thermistor on opposite sides of the inner insulating layer. The outer layer of the sensor are also bonded to the inner insulating layer around the copper foils for sealing the sensor. Stem portions of these deposited copper foils extend to edges of the insulating layers where they are electrically connected to appropriate conductors. In this arrangement, the copper foils not only serve as heat-collecting members but also serve as electrical leads extending from the thermistor. When these known sensors are located within motor windings, the heat-collecting copper foils readily conform to the winding configuration and cooperate with low thermal inertia of the thermistor to permit very rapid response of the sensor to rising motor temperatures thereby providing desired motor protection. Such sensors are described in U.S. Pat. Nos. 3,521,212 and 3,646,494 filed Jun. 21, 1968 and Jan. 23, 1970 respectively assigned to assignor of the instant application and incorporated herein by reference.
These sensors are still useful in many applications but are generally expensive to manufacture and subject to failure due to a break in electrical connection between the thermistor and the copper foil and external lead wires due to shock forces to the sensor or lead wire pull-out. Such a failure of the sensor can easily result in the loss of the entire motor winding.